Electrical switches make and break connections with incoming power conductors in switchgear handling heavy currents powering large motors in industrial and commercial settings. The switching of heavy currents produces arcing between the switch contacts, having the potential to cause considerable damage to the contacts and injury to operators. An arc flash is the rapid release of energy due to an arcing fault between phases, neutral or ground contacts. At the start of opening an electrical switch, the area of the switch contacts that carries the electrical current diminishes, causing resistive heating and melting of the metal contact material in that area. When the contacts begin to actually separate, the electrical field strength in the small gap between the contacts is quite large and causes the air molecules to ionize, forming a plasma. The positively charged ions and negative electrons of the plasma are accelerated in the high electric field toward the respective contacts of opposite polarity and strike the metallic surfaces, causing spallation, evaporation and ionization of the metal atoms. An arc then forms between the contacts, along the conductive path created by the plasma and metal vapor. Metal atoms are eroded and ionized from the contact with the more positive potential, and are accelerated toward and deposited on the contact with the more negative potential (that temporarily exist at that particular moment in an AC cycle), resulting in arc erosion. The resulting arc flash has the potential to cause considerable damage, including arcing-induced erosion of the contacts and injury to operators. The temperature of an arc flash may be capable of vaporizing metal and sending a blast of plasma and molten metal in all directions with extreme force. Damage may be caused to the switchgear both by the explosion of the arc flash and by the heat radiating from the blast. It is important to minimize the potential for harm to equipment and people by containing and redirecting the arc energy out from the switchgear.
Safety switches generally include an enclosure or electrical cabinet having a door that is pivotally mounted to the front of the cabinet to provide access to separable contacts of an electrical switch mounted inside the cabinet. An example of separable contacts of an electrical switch may be seen in blade or knife-type electrical switches. The circuit for each phase being switched is completed through a pivotable, electrically conductive knife or blade that engages a corresponding pair of electrically conductive jaws to electrically connect the line current to the load. The blade and the jaws form the separable contacts of the electrical switch. In a safety switch, the blade-type switch is mounted in an electrical cabinet, which may incorporate an insulating base to carry an incoming line terminal for each phase. An example of such blade-type electrical switch is disclosed, for example, in U.S. Pat. No. 6,331,684, to Hamid S. Abroy et al., which is incorporated herein by reference. A handle or other actuator may be mounted to the exterior of the cabinet to move the blade to connect or disconnect it with the jaws of the electrical switch. In some currently designed safety switches, the point of separation of the blade from the jaws takes place in a small area on the blade, causing resistive heating and melting of the metal contact material in that area. When the contacts begin to actually separate, an arc flash forms between the contacts, explosively disbursing a plasma and hot metal vapor. The arc flash may be guided through an arc suppression housing to attenuate, suppress and extinguish the arc flash.
An example of an arc suppression housing that provides capability to passively attenuate and extinguish arc flash events, is described in U.S. Pat. No. 8,476,546, to Hamid S. Abroy et al., which is incorporated herein by reference. A switch assembly includes an arc suppressing housing mounted in an electrical cabinet. The arc suppressing housing has opposing walls forming an arc extinguishing chamber, with an elongated notch in one wall that is shaped and sized to allow the electrically conductive knife or blade of the switch to freely pass through the arc suppressing housing and engage the electrically conductive jaws. The arc suppressing housing has a plurality of shelves between the opposing sidewalls. A plurality of arc suppressing plates extend through the housing and are seated on the shelves. The arc suppression housing and blades effectively surround the blade and jaws to quench electrical arc flashes released when the blade engages or disengages the jaws and to protect the other components in the switch assembly. The arc suppressing plates are configured to extinguish electrical arc flashes between the blade and the jaws.
Arc suppression housings are an important part of a safety switch, but typically are removed by installers in the field for wiring attachment to the terminals of the switch. Wiring diagrams and warning labels may be provided to remind the installer to re-install the housing, but such warnings are not 100% full proof and the arc suppression housings may be misplaced or not properly re-installed in the switch.